U.S. patent number 7,192,802 [Application Number 10/976,594] was granted by the patent office on 2007-03-20 for ald zno seed layer for deposition of zno nanostructures on a silicon substrate.
This patent grant is currently assigned to Sharp Laboratories of America, Inc.. Invention is credited to John F. Conley, Jr., Lisa H. Stecker.
United States Patent |
7,192,802 |
Stecker , et al. |
March 20, 2007 |
ALD ZnO seed layer for deposition of ZnO nanostructures on a
silicon substrate
Abstract
Zinc-oxide nanostructures are grown without using a metal
catalyst by forming a seed layer of polycrystalline zinc oxide on a
surface of a substrate. The seed layer can be formed by an atomic
layer deposition technique. Growth of at least one zinc-oxide
nanostructure is induced on the seed layer. The seed layer can
alternatively be formed by using a spin-on technique, such as a
metal organic deposition technique, a spray pyrolisis technique, an
RF sputtering technique or by oxidation of the seed layer.
Inventors: |
Stecker; Lisa H. (Vancouver,
WA), Conley, Jr.; John F. (Camas, WA) |
Assignee: |
Sharp Laboratories of America,
Inc. (Camas, WA)
|
Family
ID: |
36260848 |
Appl.
No.: |
10/976,594 |
Filed: |
October 29, 2004 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20060091499 A1 |
May 4, 2006 |
|
Current U.S.
Class: |
438/57;
257/E21.463; 257/E51.016; 257/E51.029; 438/104 |
Current CPC
Class: |
C30B
25/02 (20130101); C30B 29/16 (20130101); C30B
29/605 (20130101); H01L 21/02472 (20130101); H01L
21/02513 (20130101); H01L 21/02554 (20130101); H01L
21/02603 (20130101); H01L 21/0262 (20130101); H01L
21/02628 (20130101) |
Current International
Class: |
H01L
21/00 (20060101) |
Field of
Search: |
;438/57,104
;257/E51.016,E51.029 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Article entitled, "Vapor-Liquid-Solid Mechanism of Single Crystal
Growth" by R.E. Wagner et al., published in Applied Physics
Letters, Mar. 1, 1964, vol. 4, No. 5, pp. 89-90. cited by other
.
Article entitled, "Nanoscale Science and Technology" Building a Big
Future from Small Things, by C. M. Kieber, published in MRS
Bulleting/Jul. 2003, pp. 486-491. cited by other .
Article entitled, "Controlled Growth of ZnO Nanowires and Their
Optical Properties", by P. Yang et al., published in Adv. Funct.
Mater. 2002, 12, No. 5, May, pp. 323-331. cited by other .
Article entitled, "Room-Temperature Ultraviolet Nanowire
Nanolasers", by M. H. Huang et al., published in Science Mag., vol.
292, Jun. 8, 2001, pp. 1897-1899. cited by other.
|
Primary Examiner: Toledo; Fernando L.
Attorney, Agent or Firm: Ripma; David C.
Claims
What is claimed is:
1. A method of forming a zinc-oxide nanostructure, comprising:
providing a substrate; forming a seed layer of polycrystalline zinc
oxide on a surface of the substrate using an atomic layer
deposition technique; and inducing growth of at least one
zinc-oxide nanostructure on the seed layer.
2. The method according to claim 1, wherein forming the seed layer
further includes forming the seed layer using alternating pulses of
a diethylzinc precursor and water vapor.
3. The method according to claim 1, wherein the seed layer is at
least about 0.5 nm thick.
4. A zinc-oxide nanostructure formed by: providing a substrate;
forming a seed layer of polycrystalline zinc oxide on a surface of
the substrate using an atomic layer deposition technique; and
inducing growth of at least one zinc-oxide nanostructure on the
seed layer.
5. The zinc-oxide nanostructure according to claim 4, wherein
forming the seed layer further includes forming the seed layer
using alternating pulses of a diethylzinc precursor and water
vapor.
6. The zinc-oxide nanostructure according to claim 4, wherein the
seed layer is at least about 0.5 nm thick.
7. A zinc-oxide nanostructure, comprising: a substrate; a seed
layer of polycrystalline zinc oxide formed on a surface of the
substrate wherein the seed layer is formed by an atomic layer
deposition technique; and at least one zinc-oxide nanostructure
formed on the seed layer.
8. The zinc-oxide nanostructure according to claim 7, wherein the
seed layer is further formed by using alternating pulses of a
diethylzinc precursor and water vapor.
9. The zinc-oxide nanostructure according to claim 7, wherein the
seed layer is at least about 0.5 nm thick.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to nanotechnology and/or
microelectronics. In particular, the present invention relates a
method for forming zinc-oxide (ZnO) nanostructures on a silicon
(Si) substrate.
2. Description of the Related Art
Nanostructured materials, such as nanowires, nanorods, nanofibers,
whiskers, etc., exhibit interesting optical and electronic
properties and have been demonstrated for many applications, such
as chemical and bio sensors and detectors, LEDs, transistors,
lasers, field emitters, etc. See, for example, P. Yang et al.,
"Controlled growth of ZnO nanowires and their optical properties,"
Adv. Func. Mat. 12(5), 323 (2002) and C. M. Lieber, "Nanoscale
science and technology: Building a big future from small things,"
MRS Bulletin, pp. 486 491, (July 2003). Zinc oxide (ZnO), in
particular, exhibits many interesting properties for nanostructures
that could be useful for solid-state optoelectronic light emitters,
chemical sensors, and gas detectors.
One of the primary techniques used for forming nanostructures is
vapor-liquid-solid (VLS) growth. Other techniques, such as laser
ablation and arc discharge, have also been used to form
nanostructures. A VLS growth mechanism typically requires a metal
catalyst. At an appropriate temperature range, the catalyst forms a
liquid solution with the desired growth material. When the liquid
droplet becomes supersaturated with the desired growth material,
the desired material nucleates, resulting in growth of a
nanostructure. For example, a thin film (.about.3 nm) of a
catalyst, such as gold (Au), is often used. Nanostructures are
observed to grow wherever Au is present. Selective growth of
nanostructures is conventionally achieved by patterning the Au
catalyst either by dispersing Au nanoparticles onto a substrate, or
by evaporating Au through a patterned shadow mask.
Nevertheless, dispersing particles onto a substrate in the ultra
clean environments used for microelectronic fabrication is not
desirable. Additionally, the metals used as catalysts for
nanostructure growth are typically difficult to etch and,
consequently, are difficult to subtractively pattern. Moreover, the
metals used as catalysts are typically difficult to chemical
mechanical polish (CMP). Accordingly, nanostructure catalyst
materials are typically difficult to pattern via conventional
microelectronic processes. Further, contamination from using a
metal catalyst is also a concern. Accordingly, elimination of the
metal catalyst would be beneficial for reducing wafer and equipment
contamination.
Consequently, what is needed is a technique for growing ZnO
nanostructures without using a metal catalyst.
SUMMARY OF THE INVENTION
The present invention provides a technique for growing ZnO
nanostructures without using a metal catalyst.
The advantages of the present invention are provided by a method of
forming a zinc-oxide nanostructure in which a substrate is
provided, a seed layer of polycrystalline zinc oxide that is at
least about 0.5 nm thick is formed on a surface of the substrate,
and growth of at least one zinc-oxide nanostructure is induced on
the seed layer. In one exemplary embodiment of the present
invention, the seed layer is formed by an atomic layer deposition
(ALD) technique, such as by using alternating pulses of a
diethylzinc precursor and water vapor. According to the present
invention, inducing growth of at least one zinc-oxide nanostructure
includes exposing the seed layer to zinc vapor in the presence of a
trace amount of oxygen. The zinc vapor can be formed by
carbothermal reduction of zinc oxide. In another exemplary
embodiment of the present invention, the seed layer is formed by
using a spin-on technique, such as a metal organic deposition (MOD)
technique, a spray pyrolisis technique, an RF sputtering technique
or by oxidation of the seed layer.
The present invention also provides a zinc-oxide nanostructure that
is formed by forming a seed layer of polycrystalline zinc oxide
that is at least about 0.5 nm thick on a surface of a substrate,
and inducing growth of at least one zinc-oxide nanostructure on the
seed layer. In one exemplary embodiment, the seed layer is formed
using an atomic layer deposition (ALD) technique, such as by using
alternating pulses of a diethylzinc precursor and water vapor. Each
zinc-oxide nanostructure can be induced by exposing the seed layer
to zinc vapor in the presence of a trace amount of oxygen. The zinc
vapor can be formed by carbothermal reduction of zinc oxide. In
another exemplary embodiment of the present invention, the seed
layer can be formed by using a spin-on technique, such as a metal
organic deposition (MOD) technique, a spray pyrolisis technique, an
RF sputtering technique or by oxidation of the seed layer.
The present invention also provides a zinc-oxide nanostructure that
includes a substrate, a seed layer that is at least about 0.5 nm
thick that is formed on a surface of the substrate, and at least
one zinc-oxide nanostructure that is formed on the seed layer. The
seed layer can be formed by an atomic layer deposition (ALD)
technique, such as by using alternating pulses of a diethylzinc
precursor and water vapor. At least one zinc-oxide nanostructure is
formed by exposing the seed layer to zinc vapor in the presence of
a trace amount of oxygen. The zinc vapor can be generated by
carbothermal reduction of zinc oxide. In an alternative embodiment
of the present invention, the seed layer is formed by a spin-on
technique, such as a metal organic deposition (MOD) technique, a
spray pyrolisis technique, an RF sputtering technique or by
oxidation of the seed layer.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is illustrated by way of example and not by
limitation in the accompanying figures in which like reference
numerals indicate similar elements and in which:
FIG. 1 depicts a flowchart for a first exemplary embodiment of a
technique for forming ZnO nanostructures according to the present
invention;
FIGS. 2A and 2B depict a sequence of cross-sectional views of a
substrate and ZnO nanostructures that are formed by the first
exemplary embodiment of a technique for forming ZnO nanostructures
according to the present invention;
FIG. 3 depicts a flowchart for a second exemplary embodiment of a
technique for forming ZnO nanostructures according to the present
invention; and
FIGS. 4A and 4B depict a sequence of cross-sectional views of a
substrate and ZnO nanostructures that are formed by the second
exemplary embodiment of a technique for forming ZnO nanostructures
according to the present invention.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
The present invention provides two techniques for achieving growth
of ZnO nanostructures on a Si substrate that avoid use of a metal
catalyst. In one exemplary embodiment of the present invention, ZnO
nanostructures are grown on atomic-layer-deposited (ALD)
polycrystalline ZnO using a vapor-solid mechanism. In another
exemplary embodiment of the present invention, ZnO nanostructures
are grown on Metal Organic Deposition (MOD) ZnO, also using a
vapor-solid mechanism. For both exemplary embodiments, the present
invention produces a more consistent and repeatable nanostructure
growth region than is obtained by using conventional techniques of
a metal catalyst or by surface roughening. Moreover, because an
eventual goal is to integrate nanostructures into a Si CMOS
process, elimination of use of a metal catalyst for growing ZnO
nanostructures also avoids metal-catalyst contamination of Si CMOS
devices, which is potentially deleterious to Si CMOS devices.
FIG. 1 depicts a flowchart for a first exemplary embodiment 100 of
a technique for forming ZnO nanostructures according to the present
invention. FIGS. 2A and 2B depict a sequence of cross-sectional
views of a substrate and ZnO nanostructures that are formed by the
first exemplary embodiment of a technique for forming ZnO
nanostructures according to the present invention. At step 101 in
FIG. 1, a clean Si <100> or Si <111> starting wafer is
used as a substrate layer 201 (FIG. 2A). At step 102, a thin seed
layer 202 of polycrystalline ZnO is deposited on the surface of
substrate layer 201 using Atomic Layer Deposition (ALD) (FIG. 2A).
For ALD, precursors are pulsed alternately into the deposition
chamber and are separated by purges. Reactions take place on the
substrate surface and are self-limiting. Film thickness is
controlled by the number of precursor pulse/purge cycles. The
self-limiting nature of the process allows for uniformity and
excellent conformality. In one exemplary embodiment, layer 202 is
formed by alternating pulses of diethylzinc (DEZ) precursor and
H.sub.20 vapor at a substrate temperature of between about
130.degree. C. and 180.degree. C. to form ALD ZnO that is about 6
nm thick. Nanostructure growth has been induced for a seed layer
thickness between about 0.5 nm and about 80 nm. In principle, any
thickness of ALD ZnO for seed layer 202 could be used.
Alternatively, other precursors, such as di-methyl zinc, zinc
acetate and zinc chloride, could be used to form ALD ZnO.
Additionally, after seed layer 202 is formed, seed layer 202 could
be annealed to modify the crystalline structure of seed layer
202.
At step 103, ZnO nanostructure growth is induced via a vapor-solid
mechanism to form nanostructures 203, shown in FIG. 2B. The wafer
structure formed by layers 201 and 202 and depicted in FIG. 2A is
exposed to Zn vapor at about 915.degree. C. for about 30 minutes
with a flow of about 30 80 sccm Ar and a trace amount of oxygen.
Zinc vapor is generated by, for example, carbothermal reduction of
ZnO power using equal parts of ZnO and graphite. In principle,
however, any method of supplying gaseous phase Zn for growing ZnO
nanostructures would be suitable.
FIG. 3 depicts a flowchart for a second exemplary embodiment 300 of
a technique for forming ZnO nanostructures according to the present
invention. FIGS. 4A and 4B depict a sequence of cross-sectional
views of a substrate and ZnO nanostructures that are formed by the
second exemplary embodiment of a technique for forming ZnO
nanostructures according to the present invention. At step 301 in
FIG. 3, a clean Si <100> or Si <111> starting wafer is
used as a substrate layer 401 (FIG. 4A). At step 302, a thin seed
layer 402 of polycrystalline ZnO is deposited on the surface of
substrate layer 401 using a spin-on technique (FIG. 4A). In one
exemplary embodiment, layer 402 is formed by a Metal Organic
Deposition (MOD) technique using zinc acetate dehydrate in
2-methoxyethanol and ethanolamine to form MOD ZnO that is about 80
nm thick. Any thickness of MOD ZnO for seed layer 402 could be
used. After spin-on coating, the MOD-deposited film was baked for
one minute at each of 100.degree. C., 200.degree. C. and
300.degree. C. to drive off residual solvent, and then be subjected
to rapid thermal annealing in dry air at 500.degree. C. for two
minutes and then at 1000.degree. C. for five minutes.
Alternatively, ZnO layer 402 could be deposited using other
methods, such as spray pyrolisis, RF sputtering, or by oxidation of
a Zn thin film on substrate 401.
At step 303, ZnO nanostructure growth is induced via a vapor-solid
mechanism to form nanostructures 403, shown in FIG. 4B. The wafer
structure formed by layers 401 and 402 and depicted in FIG. 4A is
exposed to Zn vapor at about 915.degree. C. for about 30 minutes
with a flow of about 30 80 sccm Ar and a trace amount of oxygen.
Zinc vapor is generated by, for example, carbothermal reduction of
ZnO power using equal parts of ZnO and graphite. In principle, any
method of supplying gaseous phase Zn for growing ZnO nanostructures
would be suitable.
In another exemplary embodiment of the present invention described
in detail in concurrently filed and co-owned U.S. patent
application Ser. No. (Attorney Docket No. SLA0923), entitled
"Selective Growth of ZnO Nanostructures Using a Patterned ALD ZnO
Seed Layer," invented by J. F. Conley and L. Stecker, and
incorporated by reference herein, a ZnO seed layer is patterned
prior to nanostructure growth by applying a photoresist resist
layer that is exposed and developed using a patterned mask, etched
in hydrofluoric acid (HF) and stripped of the photoresist.
Vertically aligned ZnO growth is induced via a vapor-solid
mechanism to form nanostructures that are similar to nanostructures
403, shown in FIG. 4B. ZnO nanostructure growth occurred only in
regions that were left coated with seed layer 402.
A comparison of the nanostructures grown on a seed layer formed by
using a spin-on technique with the nanostructures grown on a seed
layer formed by an ALD technique reveals variations in morphology,
such as nanostructure diameter, nanostructure length, areal density
and structure alignment. Thus, use of the same seed material
deposited using different methods can be used for tailoring
nanostructure morphology.
Although the foregoing invention has been described in some detail
for purposes of clarity of understanding, it will be apparent that
certain changes and modifications may be practiced that are within
the scope of the appended claims. Accordingly, the present
embodiments are to be considered as illustrative and not
restrictive, and the invention is not to be limited to the details
given herein, but may be modified within the scope and equivalents
of the appended claims.
* * * * *